iMAC RAM UPGRADE

Hi guys,

Trying to speed up my iMac:

iMac (Retina 4K, 21.5-inch, 2017)

3 GHz Intel Core i5

8 GB 2400 MHz DDR4

Radeon Pro 555 2048 MB

On my research I have encountered contradictory answers: Apparently it IS possible to upgrade up to 16GB (4 x 4GB DDR), but I can't find the RAM memory slot.

Seems not to be possible after all. Could anyone, please confirm?

Thank you in advance.

Alex